1. Field of Invention
This invention relates to methods and apparatus used in thermal ink jet printers.
2. Description of Related Art
A thermal ink jet print head selectively ejects droplets of ink from a plurality of drop emitters to create a desired image on an image receiving member, such as a sheet of paper. The print head typically comprises an array of the drop emitters that convey ink to the image receiving member. In a carriage ink jet print head, the print head moves back and forth relative to the image receiving member to print the image in swaths.
Alternatively, the array may extend across the entire width of the image receiving member to form a fullprint head. Fullprint heads remain stationary as the image receiving member moves in a direction substantially perpendicular to the array of drop emitters.
A thermal ink jet print head typically comprises a plurality of ink passageways, such as capillary channels. Each channel has a drop emitter and is connected to an ink supply manifold. Ink from the manifold is retained within each channel. Then, in response to an appropriate signal applied to a resistive heating element in each channel, the ink in a portion of the channel adjacent to the heating element is rapidly heated. Rapidly heating and vaporizing some of the ink in the channel creates a bubble that causes a quantity of ink, such as an ink droplet or a main ink droplet and smaller satellite drops, to be ejected from the emitter to the image receiving member. U.S. Pat. No. 4,774,530 to Hawkins, the disclosure of which is incorporated herein by reference in its entirety, shows a general configuration of a typical inkjet print head.
U.S. Pat. No. 4,791,435 to Smith et al., the disclosure of which is incorporated herein by reference in its entirety, discloses an ink jet system where a constant temperature of the print head is maintained by using the heating elements of the print head not only for ejecting ink but to maintain the temperature close to a predetermined value as well. The print head temperature is compared to thermal models of the print head to provide information for controlling the print head temperature. At low temperature, low energy pulses are sent to each channel, or nozzle, below the voltage threshold which would cause a drop of ink to be ejected. Alternatively, the print head is warmed by firing some droplets of ink into an external chamber or xe2x80x9cspittoon,xe2x80x9d rather than onto the surface of the image receiving member.
European Patent Application 0 496 525 A1, the disclosure of which is incorporated herein by reference in its entirety, discloses ink jet recording method and apparatus in which ink is ejected by thermal energy produced by a heat generating element of a recording head. In the EP 525 application, driving circuits apply plural driving pulses to the heat generating element for every ink droplet ejected. The plural driving pulses include a first driving pulse used to increase a temperature of the ink adjacent the heater without creating a bubble, and a second driving pulse subsequent to the first driving pulse to eject the ink. Additionally, a width of the first driving pulse is adjustable to change an amount of ejected ink.
European Patent Application 0 505 154 A2, the disclosure of which is incorporated herein by reference in its entirety, discloses thermal ink jet recording method and apparatus which control an ink ejection quantity by changing driving pulses supplied to the recording head based on a variation in the temperature of the recording head. A preheat pulse is applied to the ink to control the ink temperature and is set to a value which does not cause an ink bubble to form. After a predetermined time interval, a main heat pulse is applied which forms an ink bubble to eject one or more droplets, such as a main droplet and satellite droplets, of ink from the ink channel.
U.S. Pat. No. 5,519,417 to Stephany, the disclosure of which is incorporated herein by reference in its entirety, discloses a power control system for a printer which has at least one heating element for producing spots. The system includes a thermostat, disposed on a print head, that senses the temperature of the print head. The sensed temperature is used to vary pulses applied to the at least one heating element to maintain a constant spot size.
Thus, it is known to advance the firing of a print ejector by applying different pulses to a print ejector, advancing the firing after applying a firing pulse.
U.S. Pat. No. 5,917,509 to Becerra et al., the disclosure of which is incorporated herein by reference in its entirety, discloses methods and apparatus for interleaving multiple pre-pulses in a thermal ink jet printer. The pre-pulses are timed to use the periods between preheating a print head to pre-warm additional print ejectors.
This invention provides methods and apparatus for using a print head having a plurality of drop ejectors.
This invention separately provides a thermal ink jet print head circuit architecture that enables arbitrary multiple prepulsing signals to be used.
This invention separately provides systems and methods for varying the timing of pre-pulses, as well as the timing of a final or firing pulse to sequentially pre-warm and fire print ejectors.
In various exemplary embodiments, each ejector has a heating element actuatable in response to input signals to emit a quantity of ink from the print head toward an image receiving member. Pulse trains comprising of a series of pulses are used as the input signals. The pulse train can be determined based on, for example, the temperature of the print head.
In various exemplary embodiments, the sequential and cumulative firings of the prepulses and final or drop-forming pulses in the selected channels throughout the print head are performed in a manner such that the switching transients due to energizing and de-energizing drop ejectors are reduced to the level of those due to one heater element turning on or off. The transients are reduced in spite of substantial variations in print head temperature, the number of print jets used and the print image produced. The image data is loaded from the printer controller into a print data array. The heating elements are then fired in a sequence controlled by pulse trains originating in a print head controller. The pulse trains are clocked to sequence the firing of the heating elements in a manner that minimizes the change in current per unit of time.
In various exemplary embodiments of this invention, using multiple pre-pulse wave forms allows drop mass to be stable over substantial temperature and pulse train ranges. The print head circuit design accepts these arbitrary wave forms while decreasing switching noise, reducing fluidic cross-talk in the print head, and allowing maximal droplet ejection frequencies.
Other objects, advantages and features of the invention will become apparent from the following detailed description taken in conjunction with the attached drawings, which disclose exemplary embodiments of the invention.